Several types of sampling devices which separate entrained particles from a gaseous medium according to size are available on the market today. Such devices are capable of separating microscopic size particles according to mean particle diameter on the various stages of the device. Examples of such devices are illustrated in U.S. Pat. Nos. 3,693,457 and 3,795,135. One of the problems with such sampling devices, however, is that there is a tendency to re-entrain the particles collected so that the sample is not truly representative of the particles within the gaseous medium. Further, difficulties have been encountered with the use of such sampling devices in that the flow distribution of such devices tended to be unevenly spaced about each stage. Another problem with these devices is that the weighing operation used to quantify the sample collected is difficult.